The major goal of the proposed study is to understand the mechanisms by which the interaction of MHC/self-peptide complex with T cell antigen receptor may regulate the development of type 1 diabetes. Type 1 diabetes is a beta cell-specific; T cell mediated autoimmune disease. Destruction of the insulin producing (beta) cells of the pancreas by T cells can lead to the development of insulin-dependent diabetes mellitus (IDDM) in humans. More than one gene may contribute to the onset of the autoimmune disease, but the major histocompatibility complex (MHC) class II genotype is the most important genetic factor determining disease susceptibility. Nonobese diabetic (NOD) mice develop autoimmune diabetes that is similar to that in humans. These mice express a unique MHC class II I-A allele, I-Ag7; the homologue to human diabetes associated DQ molecules. It is necessary for I-Ag7 to be present in both alleles for the development of diabetes. Expression of resistant MHC class II alleles in the NOD mouse protects them from diabetes. However, it is not clear how the expression of I-Ag7 and its interaction with T cell receptors may lead to the development of diabetes. The hypothesis is that selective presentation of self-peptides by I-Ag7 may select and/or stimulate autoreactive pathogenic T cells, which lead to T cell-mediated autoimmune diabetes. Experiments in Specific Aim A are designed to develop in vitro tools to identify antigen specific T cells in NOD mice. Soluble multivalent I-Ag7 complexes with covalently linked peptides will be generated, labeled, and used as staining reagents. These labeled soluble proteins will then be used in experiments in Specific Aim B to detect antigen specific T cells, and to identify and characterize diabetogenic T cells derived from NOD mice. Identification of diabetogenic T cells and their specific diabetogenic antigens will allow for further studies to determine the roles of diabetogenic peptides and T cells, and regulatory mechanisms underlying immune responses leading to type 1 diabetes.